package leetcode;

public class LeetCode21 {

    //老掉牙的办法
    synchronized public ListNode mergeTwoLists2(ListNode l1, ListNode l2) {
        ListNode p = new ListNode(0), result = p;
        while (l1 != null && l2 != null) {
            if (l1.val < l2.val) {
                p.next = new ListNode(l1.val);
                l1 = l1.next;
            } else {
                p.next = new ListNode(l2.val);
                l2 = l2.next;
            }
            p = p.next;
        }
        while (l1 != null) {
            p.next = new ListNode(l1.val);
            l1 = l1.next;
            p = p.next;
        }
        while (l2 != null) {
            p.next = new ListNode(l2.val);
            l2 = l2.next;
            p = p.next;
        }
        return result.next;
    }

    //------------------------------------------------------------------
    //迭代
    public ListNode mergeTwoLists1(ListNode l1, ListNode l2) {
        ListNode p = new ListNode(0), result = p;

        return result.next;
    }

    //递归
    public ListNode mergeTwoLists(ListNode l1, ListNode l2) {
        if (l1 == null) {
            return l2;
        } else if (l2 == null) {
            return l1;
        } else if (l1.val < l2.val) {
            l1.next = mergeTwoLists(l1.next, l2);
            return l1;
        } else {
            l2.next = mergeTwoLists(l1, l2.next);
            return l2;
        }
    }
}
